(1) Field of the Invention
The present invention relates to arrangements concerning installing a supply of fuel on board a rotorcraft for the purpose of feeding fuel to at least one fuel-burning engine of the rotorcraft. The present invention relates more particularly to ways of mounting pouches on board a rotorcraft, which pouches form fuel tanks installed in the substructure of the fuselage of the rotorcraft.
(2) Description of Related Art
Rotorcraft are aircraft having one or more rotary wings including at least one main rotor of substantially vertical axis, and possibly also at least one rotor of substantially horizontal axis such as a tail rotor or a propulsive propeller. The rotor(s) of a rotorcraft are conventionally driven in rotation by a power plant comprising one or more fuel-burning engines, and in particular turboshaft engines.
The engines are fed individually with fuel by respective fuel circuits. For each fuel circuit, the fuel is delivered to an engine from a fuel tank installed on board the rotorcraft and serving to feed a given engine with fuel.
More particularly, a fuel feed unit of a power plant of a rotorcraft includes one or more fuel feed assemblies. In a single-engine rotorcraft, a single fuel feed assembly is provided for the single engine of the rotorcraft. In a rotorcraft having a plurality of engines, such as a twin-engine rotorcraft for example, the fuel feed assemblies are allocated respectively to each of the engines in order to enable them to operate independently.
Any given fuel feed assembly mainly comprises a fuel tank and a feeder that retains some minimum quantity of fuel. Depending on the ways in which the tank is installed on board the rotorcraft, the tank may comprise a single pouch or it may be made up of a plurality of distinct pouches that are put into fluid flow communication with one another. The feeder is formed by an enclosure that is independent with respect to free fluid flow communication for fuel between the tank and the feeder. The capacity of the feeder is limited to an amount that is sufficient to enable flight to continue for at least a predetermined duration in the event of a failure of the rotorcraft.
The fuel circuit for feeding fuel to the power plant takes fuel from inside the feeder in order to deliver it to the associated engine by means of a feed pump incorporated in the power plant and driven by the engine, and/or possibly by means of at least one booster pump immersed in the feeder. The feeder is fed with fuel from the tank by a fuel supply circuit making use of a supply pump associated with an ejector immersed in the tank. Such a supply pump may possibly be formed by a said booster pump. An overflow device restores excess fuel to the tank by allowing it to overflow from the feeder.
With a rotorcraft having a plurality of engines fed with fuel by respective fuel feed assemblies, the various tanks are placed in fuel flow communication with one another via a transfer circuit for transferring fuel from one tank to another. Such a transfer circuit makes use in particular of a transfer pump, which may be operated in order to balance the quantities of fuel contained in respective different tanks and/or in order to enable all of the on-board fuel to be used for feeding fuel to any one of the engines from the tank that is associated therewith.
By way of example, reference may be made to Document EP 2 567 896 (Eurocopter France), which describes such a fuel feed unit for a power plant of a rotorcraft.
There exists a problem of installing and maintaining the fuel feed unit. Clearly account needs to be taken not only of the arrangement of the fuel supply and the specific ways in which it is used, but also of the ways in which the various members included in such a fuel feed unit are arranged and operate.
In a known solution, as described in Document U.S. Pat. No. 5,451,015 (Bell Helicopter Textron Inc.), a compartment housing the supply of fuel is provided behind the cockpit of the rotorcraft vertically on the axis of rotation of the main rotor.
In another known solution as described by Documents FR 2 756 255 (Eurocopter France) and EP 2 567 896 (Eurocopter France), the supply of fuel is stored in fuel pouches arranged in respective compartments arranged in the substructure or bottom section (tub) of the fuselage of the rotorcraft. The various fuel pouches in a given said fuel feed assembly are in free fluid flow communication with one another via specific arrangements commonly referred to as “intercommunication”.
With the fuel supply installed in such a configuration, the various fuel pouches of one or more tanks are placed under an equipment floor providing separation between the bottom section and the cabin of the rotorcraft. Such an equipment floor is supported in various ways by reinforcement fastened to the fuselage of the rotorcraft, so as to provide a loading surface inside the cabin of the rotorcraft that is located above compartments for receiving fuel pouches.
More particularly, such equipment floors in an aircraft are commonly fastened to load-carrying members mounted on the fuselage of the aircraft. By way of example, such load-carrying members are constituted by beams, cross-members, and/or support legs supported by the fuselage. By way of example, reference may be made on this topic to the following Documents FR 2 933 065 (Airbus France SAS), FR 2 957 050 (EADS France), FR 2 984 273 (Aerolia SAS), and FR 2 947 524 (Airbus Operations SAS), which describe various ways of mounting such an equipment floor on board an aircraft.
The solution of placing tanks in the bottom section of a rotorcraft makes it possible to have a considerable volume for installing the fuel supply. The quantity of fuel loaded on board is advantageously optimized while also obtaining natural balancing of the weight of on-board fuel relative to the axis of rotation of the main rotor of the rotorcraft that essentially provides the rotorcraft with lift. This constant search to carry an optimized quantity of fuel on board a rotorcraft is mentioned in Document U.S. Pat. No. 3,966,147 (Grumman Aerospace Corp.).
Furthermore, an advantage of placing tanks in the bottom section of a rotorcraft makes it possible to keep the tanks as far away as possible from the power plant. These arrangements serve to improve safety of the aircraft in terms of carrying fuel, since the fuel is located at a distance from a sensitive zone of the rotorcraft including the main rotor of the rotorcraft and the power plant, which generates heat.
It is also known to install fuel tanks laterally outside the fuselage of a rotorcraft, which tanks are carried by the fuselage. On this topic, reference may be made for example to Document U.S. Pat. No. 4,860,972 (Era Aviat. Inc.) and to above-mentioned Document U.S. Pat. No. 3,966,147 (Grumman Aerospace Corp.).
Nevertheless, and in general, installing and maintaining the supply of fuel inside the fuselage of a rotorcraft remain difficult. The volume available in a rotorcraft that is used for transporting people and freight needs to be maximized, to the detriment of easy access to compartments providing equipment space such as the compartments housing the supply of fuel. Consequently, the compartments for receiving fuel pouches are often difficult for an operator to access.
On this topic, reference may be made to Document U.S. Pat. No. 5,371,935 (United Tech. Corp.) which relates to such difficulties of access to compartments for receiving fuel pouches, or indeed to the above-mentioned Document U.S. Pat. No. 3,966,147 (Grumman Aerospace Corp.), which proposes avoiding such access difficulties by mounting main fuel tanks laterally outside the fuselage.
Specifically, easy access to compartments for receiving fuel pouches depends on the actual structure of the fuselage of the rotorcraft. Rotorcraft fuselages are essentially made up of stiffener members for stiffening a covering, which members are arranged and fastened together so as to impart a desired shape to the fuselage. The stiffener members and more or less locally the covering are mechanically load-bearing relative to the general forces supported by the fuselage.
In order to shape the fuselage, each transverse stiffener member is formed by a frame that locally defines the transverse profile of the fuselage. Such frames, which may be distinct structures of distinct shapes, are typically spaced apart from one another in the longitudinal direction of the fuselage between the front and the rear of the rotorcraft. Longitudinal stiffeners such as folded or extruded section members, referred to as “stingers” or as “longerons”, stabilize the covering and the framework of the fuselage.
Conventionally, said general forces supported by the fuselage are generated amongst other things at least by the lift and the propulsion of the rotorcraft. A load-bearing top floor is anchored to at least two middle frames that longitudinally define a middle segment of the fuselage lying between a cockpit and a tail boom of the rotorcraft. The top floor forms a top wall of the fuselage, extending at least in part along said middle segment and it supports the main rotor via a main gearbox (MGB), together with at least part of the power plant.
Also conventionally when the supply of fuel is housed in the substructure of the fuselage of the rotorcraft, said general forces supported by the fuselage may possibly be generated by the weight of fuel contained in the fuel pouches. As a result, fuel pouches are conventionally supported by the bottom face of the rotorcraft, or rotorcraft belly, which is formed by the covering of the fuselage.
In this context, it is necessary to provide hatches in the equipment floor in order to enable an operator to access the compartments arranged in the bottom section of the rotorcraft for receiving fuel tanks Nevertheless, the use of such hatches is awkward and special provisions must be arranged to facilitate access to the tank by an operator, such as for example in the manner described in Document U.S. Pat. No. 5,371,935 (United Tech. Corp.).
Furthermore, a drawback of receiving the tanks in the bottom section of the fuselage lies in difficulties of providing various passages for fuel, such as from one tank to another, from one pouch to another within a single tank, and/or between the feeders and the respective tanks that are associated therewith.
Such fuel passages involve weakening the frames through which said passages need to be provided. Since the frames are structures that need to provide the strength desired for the fuselage relative to the general forces to which it is subjected, weakening the frames requires them to be specially reinforced, consequently increasing their weight and making their structure more complex.
Furthermore, account needs to be taken of a situation in which the rotorcraft is involved in a crash, in order to protect personnel and goods on board the rotorcraft. Installing tanks in compartments of the fuselage makes such protection difficult, as mentioned by the above-mentioned Document U.S. Pat. No. 3,966,147 (Grumman Aerospace Corp.).
Account also needs to be taken of the constant search in aviation for simplifying equipment on board an aircraft, in particular for the purposes of reducing its weight and simplifying maintenance operations.
It should naturally be understood that the concepts of “vertical”, “horizontal”, “longitudinal”, “transverse”, “front”, “rear”, “bottom”, “top”, and “overlying” are relative terms to be understood relative to the situation of the rotorcraft when standing on the ground and to the long direction of the fuselage between the front and the rear of the rotorcraft. Such concepts are commonly understood by the person skilled in the art.
Furthermore, in the context of a rotorcraft fuselage, the concept of “load-bearing” and “non-load-bearing” are concepts qualifying members of the rotorcraft in widespread use by the person skilled in the art, such concepts specifying whether members of the fuselage do or do not bear loads relative to the general forces to which the fuselage is subjected.
The person skilled in the art is continuously searching for ways to organize how the unit for feeding fuel to one or more engines of a rotorcraft is to be installed onboard the rotorcraft in the light of a multitude of problems to be solved and of difficulties to be overcome. The person skilled in the art is continuously searching for solutions that provide a satisfactory compromise between the various drawbacks and advantages associated with such solutions.